1. Field of the Invention
The present invention relates to a belted radial ply tire improved in directional stability during straight running.
2. Description of Related Art
When a vehicle provided with radial ply tires is running straight, a phenomenon called "handle pull" is often caused. This phenomenon is such that the actual running direction of the vehicle is leaned toward one side, right or left of the intended straight running direction, which results in an inferior straight running performance.
The main cause of this phenomenon is considered to be a high residual cornering force (CF) of the tires. Here, the residual cornering force is defined as a cornering force at a slip angle at which self aligning torque (SAT) becomes zero.
In the radial ply tires having a higher cornering power (CP), for example radial ply tires provided with a steel cord belt reinforcement, the residual cornering force is likely to be a large value.
In order to decrease the residual cornering force and, thereby, to prevent the "handle pull" phenomenon, it has been employed to decrease the angle of belt cords and to decrease the rigidity of the tread pattern. However, those methods deteriorate dynamic performances of the tire or vehicles.